This study is directed toward two sets of coordinated gene responses in Drosophila, the "heat shock" response and the production of muscle-specific proteins during myogenesis. Both of these gene responses can be experimentally manipulated and both can, we believe, serve as model systems for the kinds of changes in genetic activity that occur during cell determination and differentation in higher organisms. The very limited transcription during the heat shock response presents an ideal situation for characterization of a population of nuclear RNAs. We have selected a library of recombinant DNA molecules complementary to heat shock nuclear RNA. These will be characterized with respect to chromosomal location, gene structure and the fate of the complementary RNA. We have developed a cell-free protein system from lysates of Drosophila cells. Such lysates prepared from heat shocked cells display the translational control that is induced by heat shock. These lysates are being used to investigate the molecular basis of this translation control. We have developed a technique for obtaining myogenic development in mass cultures of dissociated gastrula stage embryos. These cultures are being used to characterize muscle proteins and their mRNAs. Using these mRNAs we have isolated several clones of recombinant DNA coding for proteins in Drosophila muscle. A persistent virus of the Schneider 2-L cell line is being characterized. Its interactions with the cell line and other Drosophila tissues are being studied.